The present invention relates to a developer supplying member for supplying developer to a developer supporting member; a developing device having the developer supporting member for developing a toner image on a recording medium; and an image forming apparatus having the developing device for developing and outputting image data input thereto on the recording medium according to a specific control. Further, the present invention relates to a method of producing a developer supplying member.
In a conventional image forming apparatus such as a printer, a copier, a facsimile, an electro photography color recording apparatus, and the likes, a charging device uniformly charges a surface of an image supporting member. After an exposure device forms a static latent image on the surface of the image supporting member according to image information, a developer supplying member supplies developer as toner to a developer supporting member, so that the developer supporting member attaches developer to the image supporting member to form a toner image. After the toner image is transferred to a recording medium, a fixing device fixes the toner image, thereby forming the toner image on the recording medium.
In the conventional image forming apparatus, in order to prevent a blurred image or a reduction in a print density in the image developed on the recording medium, the developer supplying member may include a foamed layer using a foamed member formed of discrete foams (refer to Patent Reference).    Patent Reference: Japanese Patent Publication No. 07-333996
In the conventional developer supplying member including the foamed layer using the foamed member formed of the discrete foams as disclosed in Patent Reference, it is necessary to perform a foaming process and a vulcanization process using a small mold metal. Accordingly, an operation of a manufacturing machine tends to be complex, and it is difficult to increase productivity per unit time. Further, it is difficult to reduce a thickness of a foam call wall of the foamed member. Accordingly, it is difficult to decrease hardness of the foam cell wall, so that a frictional load relative to developer tends to increase, thereby easily damaging developer.
In contrast, in order to improve productivity and reduce the frictional load relative to developer, when the developer supplying member includes a foamed layer using a foamed member formed of continuous foams with low hardness, developer tends to fill in the foamed member formed of the continuous foams as the number of print sheets increases, thereby increasing a volume resistivity of the developer supplying member.
When the volume resistivity of the developer supplying member increases, an electric field intensity to be charged into a toner layer formed of developer decreases between the developer supporting member and the developer supplying member, thereby decreasing a charge amount of developer. When the charge amount of developer decreases, developer may be attached to the developer supporting member with a weaker attraction force. Accordingly, when a developing blade slides against developer to form the toner layer on a developing roller, the formation of the toner layer tends to be unstable, thereby causing a blurred text or reduction in a print density in the image data developed on the recording medium.
In view of the problems described above, an object of the present invention is to provide a developer supplying member, a developing device, and an image forming apparatus capable of solving the problems of the conventional developer supplying member. In the present invention, a volume resistivity of the developer supplying member is controlled. Accordingly, even when the number of print sheets increases, it is possible to prevent a blurred text or reduction in a print density in an image data developed on a recording medium.
Further objects and advantages of the invention will be apparent from the following description of the invention.